Rate,   Load  and  Load Rate

There are many definitions on the web as to what spring rate, load and load rate are,and most are wrong. As a spring manufacturer since 1937 we kind of think we know just a bit more than most. No brag, just a fact.

The biggest misunderstanding is between the terms Rate and Load Rate. While they sound the same they are not the same.

While it is a bit more involved, Rate can be simply stated as the amount of weight required to deflect a spring (any spring) one-inch. The lower the rate, the softer the spring. The softer the spring the smoother the ride.

Load Rate on the other hand is the amount of weight a spring is designed to carry when it is deflected to a certain height. A better term would be Rated Load or better yet the term we use, Design Load.

Because rate is the amount of weight required to deflect a spring one-inch and load rate is the amount of weight a spring is designed to carry you can now understand why the two terms are not interchangeable. In many cases the design load has nothing to do with how much weight the spring will really be carrying. Design load is a number chosen for whatever reason by the spring engineer.

Then what does Load mean?  Load is the amount of weight that is really on the spring.

An example of all of this would be a leaf spring that has a Free Arch of 6-inches, a Rate of 200 lbs and is Designed to carry 600 lbs when it is deflected to 3-inches. But is is only carrying 400 lbs.

So the correct way to describe this leaf spring would be:

Rate is 200 lbs - Load Rate or Design Load is 600 lbs - Load of 400 lbs

All of the above terms apply to all springs, leaf, coil, steel, rubber and air.

To learn more about Leaf and Coil Springs read our Spring Tech 101 Booklet.